I really like the concept of this one. I feel like this almost all the time! I like how you added blush to her cheeks and how she leans on her arm. Most of your mistakes would have to be in the proportions and anatomy. I myself am not exactly the best at proportions and anatomy, but I can see a few things that you could fix in the future.

Mainly, the cheeks should flow into/overlap the actual eyes a bit more, and your should watch out where you attach your arms. Try drawing out a horizontal line both at the top and bottom of the shoulders and try keeping the base of the arm in there.

Also, the paper looks as though its on the other side of a wall, try making the two corners closer to the viewer farther apart from the ones farther away.

Over all, I'd say that this is a very adorable style and idea. I love it.